From a8a2ebe9e729f69dc5775dee33cde1d5067a880a Mon Sep 17 00:00:00 2001
From: Alp Toker <alp@nuanti.com>
Date: Tue, 22 Oct 2013 22:53:01 +0000
Subject: [PATCH] Retain previous language linkage of friend function
declarations
With this extension, friend function declarations will retain the language
linkage specified for previous declarations instead of emitting an error
diagnostic.
The feature is known to be compatible with GCC and MSVC and permits a
language to be specified indirectly where it cannot otherwise be written
directly in class scope.
Work is ongoing to improve linkage spec diagnostics.
Fixes PR17337.
Reviewed by Richard Smith.
git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193206 91177308-0d34-0410-b5e6-96231b3b80d8
---
include/clang/Basic/DiagnosticSemaKinds.td | 3 +++
lib/Sema/SemaDecl.cpp | 19 ++++++++++++++++---
test/SemaCXX/linkage-spec.cpp | 19 +++++++++++++++++++
3 files changed, 38 insertions(+), 3 deletions(-)
diff --git a/include/clang/Basic/DiagnosticSemaKinds.td b/include/clang/Basic/DiagnosticSemaKinds.td
index f10cae41cb7..7abb74cd0b7 100644
--- a/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3581,6 +3581,9 @@ def err_static_non_static : Error<
"static declaration of %0 follows non-static declaration">;
def err_different_language_linkage : Error<
"declaration of %0 has a different language linkage">;
+def ext_retained_language_linkage : Extension<
+ "friend function %0 retaining previous language linkage is an extension">,
+ InGroup<DiagGroup<"retained-language-linkage">>;
def err_extern_c_global_conflict : Error<
"declaration of %1 %select{with C language linkage|in global scope}0 "
"conflicts with declaration %select{in global scope|with C language linkage}0">;
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 81ade1f3ce0..80f95e68690 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -2607,9 +2607,22 @@ bool Sema::MergeFunctionDecl(FunctionDecl *New, Decl *OldD, Scope *S,
}
if (haveIncompatibleLanguageLinkages(Old, New)) {
- Diag(New->getLocation(), diag::err_different_language_linkage) << New;
- Diag(Old->getLocation(), PrevDiag);
- return true;
+ // As a special case, retain the language linkage from previous
+ // declarations of a friend function as an extension.
+ //
+ // This liberal interpretation of C++ [class.friend]p3 matches GCC/MSVC
+ // and is useful because there's otherwise no way to specify language
+ // linkage within class scope.
+ //
+ // Check cautiously as the friend object kind isn't yet complete.
+ if (New->getFriendObjectKind() != Decl::FOK_None) {
+ Diag(New->getLocation(), diag::ext_retained_language_linkage) << New;
+ Diag(Old->getLocation(), PrevDiag);
+ } else {
+ Diag(New->getLocation(), diag::err_different_language_linkage) << New;
+ Diag(Old->getLocation(), PrevDiag);
+ return true;
+ }
}
if (OldQTypeForComparison == NewQType)
diff --git a/test/SemaCXX/linkage-spec.cpp b/test/SemaCXX/linkage-spec.cpp
index bdc217d9c8c..1598d0e35a0 100644
--- a/test/SemaCXX/linkage-spec.cpp
+++ b/test/SemaCXX/linkage-spec.cpp
@@ -1,4 +1,5 @@
// RUN: %clang_cc1 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -fsyntax-only -verify -Wretained-language-linkage -DW_RETAINED_LANGUAGE_LINKAGE %s
extern "C" {
extern "C" void f(int);
}
@@ -154,3 +155,21 @@ void bar_pr7927() {
::f_pr7927(E_7927);
::f_pr7927(0);
}
+
+namespace PR17337 {
+ extern "C++" {
+ class Foo;
+ extern "C" int bar3(Foo *y);
+ class Foo {
+ int x;
+ friend int bar3(Foo *y);
+#ifdef W_RETAINED_LANGUAGE_LINKAGE
+// expected-note@-5 {{previous declaration is here}}
+// expected-warning@-3 {{retaining previous language linkage}}
+#endif
+ };
+ extern "C" int bar3(Foo *y) {
+ return y->x;
+ }
+ }
+}
--
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